Extracellular acidosis has been demonstrated to play a key role in the process of metabolic depression under long-term environmental stress, exemplified in the marine invertebrate Sipunculus nudus. These findings led to the hypothesis that acid-base regulation is associated with a visible cost depending on the rate and mode of H(+)-equivalent ion exchange. To test this hypothesis, the effects of different ion-transport inhibitors on the rate of pH recovery during hypercapnia, on energy turnover and on steady-state acid-base variables were studied in isolated body wall musculature of the marine worm Sipunculus nudus under control conditions (pHe 7.90) and during steady-state extracellular acidosis (pHe 7.50 or 7.20) by in vivo (31)P-NMR and oxygen consumption analyses. During acute hypercapnia (2 % CO(2)), recovery of pHi was delayed at pHe 7.5 compared with pHe 7.9. Inhibition of the Na(+)/H(+)-exchanger by 5-(N,N-dimethyl)-amiloride (DMA) at pHe 7.5 delayed recovery even further. This effect was much smaller at pHe 7.9. Inhibition of anion exchange by the addition of the transport inhibitor 4, 4′-diisothiocyanatostilbene-2,2′-disulphonic acid (DIDS) prevented pH recovery at pHe 7.5 and delayed recovery at pHe 7.9, in accordance with an effect on Na(+)-dependent Cl(−)/HCO(3)(−) exchange. The effects of ouabain, DIDS and DMA on metabolic rate were reduced at low pHe, thereby supporting the conclusion that acidosis caused the ATP demand of Na(+)/K(+)-ATPase to fall. This reduction occurred via an inhibiting effect on both Na(+)/H(+)- and Na(+)-dependent Cl(−)/HCO(3)(−) (i.e. Na(+)/H(+)/Cl(−)/HCO(3)(−)) exchange in accordance with a reduction in the ATP demand for acid-base regulation during metabolic depression. Considering the ATP stoichiometries of the two exchangers, metabolic depression may be supported by the predominant use of Na(+)/H(+)/Cl(−)/HCO(3)(−) exchange under conditions of extracellular acidosis.

Aronson
P. S.
,
Suhm
M. A.
,
Nee
J.
(
1983
).
Interaction of external H+with the Na+—H+exchanger in renal microvillus membrane vesicles
.
J. Biol. Chem
258
,
6767
–.
Bernardes
C. F.
,
Meyer-Fernandes
J. R.
,
Martins
O. B.
,
Vercesi
A. E.
(
1997
).
Inhibition of succinic dehydrogenase and F0F1-ATP synthase by 4,4-diisothiocyanatostilbene-2,2 -disulfonic acid (DIDS)
.
Z. Naturforsch
52
,
799
–.
Bianchini
L.
,
Pouyssegur
J.
(
1994
).
Molecular structure and regulation of vertebrate Na+/H+exchangers
.
J. Exp. Biol
196
,
337
–.
Bing
O. H. L.
,
Brooks
W. W.
,
Messer
J. V.
(
1973
).
Heart muscle viability following hypoxia: Protective effects of acidosis
.
Science
180
,
1297
–.
Bonventre
J. V.
,
Cheung
J. Y.
(
1985
).
Effects of metabolic acidosis on viability of cells exposed to anoxia
.
Am. J. Physiol
249
,
149
–.
Boron
W. F.
,
McCormick
W. C.
,
Roos
A.
(
1981
).
pH regulation in barnacle muscle fibers: dependence on extracellular sodium and bicarbonate
.
Am. J. Physiol
240
,
80
–.
Buck
L. T.
,
Hochachka
P. W.
(
1993
).
Anoxic suppression of Na+—K+-ATPase and constant membrane potential in hepatocytes: support for channel arrest
.
Am. J. Physiol
265
,
1020
–.
Chih
P.
,
Rosenthal
M.
,
Sick
T. J.
(
1989
).
Ion leakage is reduced during anoxia in turtle brain: a potential survival strategy
.
Am. J. Physiol
257
,
1562
–.
Doumen
C.
,
Ellington
W. R.
(
1992
).
Intracellular free magnesium in the muscle of an oxyconforming marine invertebrate: measurement and effect of metabolic and acid—base perturbations
.
J. Exp. Zool
261
,
394
–.
Ellington
W. R.
(
1989
).
Phosphocreatine represents a thermodynamic and functional improvement over other muscle phosphagens
.
J. Exp. Biol
143
,
177
–.
Fleser
A.
,
Marshansky
V.
,
Duplain
M.
,
Noel
J.
,
Hoang
A.
,
Tejedor
A.
,
Vinay
P.
(
1995
).
Cross-talk between the Na+—K+-ATPase and the H+-ATPase in proximal tubules in suspension
.
Renal Physiol. Biochem
18
,
140
–.
Grinstein
S.
,
Cohen
S.
,
Rothstein
A.
(
1984
).
Cytoplasmic pH regulation in thymic lymphocytes by an amiloride-sensitive Na+/H+antiport
.
J. Gen. Physiol
83
,
341
–.
Grinstein
S.
,
Rothstein
A.
(
1986
).
Mechanisms of regulation of the Na+/H+exchanger
.
J. Membr. Biol
90
,
1
–.
Hotta
Y.
,
Fujita
M.
,
Nakagawa
J.
,
Ando
H.
,
Takeya
K.
,
Ishikawa
N.
,
Sakakibara
J.
(
1998
).
Contribution of cytosolic ionic and energetic milieu change to ischemia-and reperfusion-induced injury in guinea pig heart: fluorometry and nuclear magnetic resonance studies
.
J. Cardiovasc. Pharmac
31
,
146
–.
Jensen
B. L.
,
Skott
O.
(
1996
).
Blockade of chloride channels by DIDS stimulates renin release and inhibits contraction of afferent arterioles
.
Am. J. Physiol
270
,
718
–.
Kahn
A. M.
,
Cragoe
E. J.
,
Allen
J. C.
,
Halligan
R. D.
,
Shelat
H.
(
1990
).
Na+—H+and Na+-dependent Cl/HCO3 exchange control pHi in vascular smooth muscle
.
Am. J. Physiol
259
,
134
–.
Kleyman
T. R.
,
Cragoe
E. J.
(
1988
).
Amiloride and its analogs as tools in the study of ion transport
.
J. Membr. Biol
105
,
1
–.
Kost
G. J.
(
1990
).
pH standardization for phosphorus-31 magnetic resonance heart spectroscopy at different temperatures
.
Magnetic Resonance Med
14
,
496
–.
Krapf
R.
,
Alpern
A. J.
(
1993
).
Cell pH and transepithelial H/HCO3transport in the renal proximal tubule
.
J. Membr. Biol
131
,
1
–.
Krumschnabel
G.
,
Biasi
C.
,
Schwarzbaum
P. J.
,
Wieser
W.
(
1996
).
Membrane—metabolic coupling and ion homeostasis in anoxia-tolerant and anoxia-intolerant hepatocytes
.
Am. J. Physiol
270
,
614
–.
Little
P. J.
,
Neylon
C. B.
,
Farrelly
C. A.
,
Weissberg
P. L.
,
Cragoe
E. J.
,
Bobik
A.
(
1995
).
Intracellular pH in vascular smooth muscle: Regulation by sodium—hydrogen exchange and multiple sodium-dependent HCO3mechanisms
.
Cardiovasc. Res
29
,
239
–.
Madshus
I. H.
(
1988
).
Regulation of intracellular pH in eucaryotic cells
.
Biochem. J
250
,
1
–.
Neylon
C. B.
,
Little
P. J.
,
Cragoe
E. J.
,
Bobik
A.
(
1990
).
Intracellular pH in human arterial smooth muscle: regulation by Na+—H+exchange and a novel 5-(N -ethyl- N -isopropyl)amiloride-sensitive Na+-and HCO3-dependent mechanism
.
Circ. Res
67
,
814
–.
Nilsson
G. E.
,
Perez-Pinzon
M.
,
Dimberg
K.
,
Winberg
S.
(
1993
).
Brain sensitivity to anoxia in fish as reflected by changes in extracellular K+activity
.
Am. J. Physiol
264
,
250
–.
Pentilla
A.
,
Trump
B. F.
(
1974
).
Extracellular acidosis protects Ehrlich ascites tumor cells and rat renal cortex against anoxic injury
.
Science
185
,
277
–.
Perez-Pinzon
M. A.
,
Rosenthal
M.
,
Sick
T. J.
,
Lutz
P. L.
,
Pablo
J.
,
Mash
D.
(
1992
).
Downregulation of sodium channels during anoxia: a putative survival strategy of turtle brain
.
Am. J. Physiol
262
,
712
–.
Pörtner
H. O.
(
1987
).
Contributions of anaerobic metabolism to pH regulation in animal tissues: theory
.
J. Exp. Biol
131
,
69
–.
Pörtner
H. O.
(
1990
).
Determination of intracellular buffer values after metabolic inhibition by fluoride and nitrilotriacetic acid
.
Respir. Physiol
81
,
275
–.
Pörtner
H. O.
,
Andersen
N. A.
,
Heisler
N.
(
1991
).
Proton equivalent ion transfer in Sipunculus nudus as a function of ambient oxygen tension: relationships with energy metabolism
.
J. Exp. Biol
156
,
21
–.
Pörtner
H. O.
,
Boutilier
R. G.
,
Tang
Y.
,
Toews
D. P.
(
1990
).
Determination of intracellular pH and P COafter metabolic inhibition by fluoride and nitrilotriacetic acid
.
Respir. Physiol
81
,
255
–.
Pörtner
H. O.
,
Reipschläger
A.
,
Heisler
N.
(
1998
).
Acid—base regulation, metabolism and energetics in Sipunculus nudus as a function of ambient carbon dioxide
.
J. Exp. Biol
201
,
43
–.
Reipschläger
A.
,
Pörtner
H. O.
(
1996
).
Metabolic depression during environmental stress: the role of extracellular versus intracellular pH in Sipunculus nudus
.
J. Exp. Biol
199
,
1801
–.
Shi
H.
,
Hamm
P. H.
,
Meyers
R. S.
,
Lawler
R. G.
,
Jackson
D. C.
(
1997
).
Mechanisms of pHi recovery from NH4Cl-induced acidosis in anoxic turtle heart: a 31P-NMR study
.
Am. J. Physiol
272
,
6
–.
Soleimani
M.
,
Bookstein
C.
,
Singh
G.
,
Rao
M. C.
,
Chang
E. B.
,
Bastani
B.
(
1995
).
Differential regulation of Na+/H+exchange and H+-ATPase by pH and HCO3in kidney proximal tubules
.
J. Membr. Biol
144
,
209
–.
Vandenberg
J. I.
,
Metcalfe
J. C.
,
Grace
A. A.
(
1994
).
Intracellular pH recovery during respiratory acidosis in perfused hearts
.
Am. J. Physiol
266
,
489
–.
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